1. Field of the Invention
This invention relates to semiconductor wafer processing systems and, more particularly, to a method and apparatus for depositing a material upon a semiconductor wafer using a transition chamber of a multiple chamber semiconductor wafer processing system.
2. Description of the Background Art
Semiconductor wafer processing systems comprised of multiple process chambers are well known in the art. Within these systems, wafers are prepared and processed through the deposition and treatment of multiple layers of conductive and semiconductive materials. Such tools process semiconductor wafers through a plurality of sequential steps to produce integrated circuits. In such tools, a plurality of process chambers and preparatory chambers are arranged in one or more clusters, each served by robotic transfer mechanism. Hence, such tools are commonly referred to as cluster tools. Such cluster tools include the Endura and Centura systems manufactured by Applied Materials, Inc. of Santa Clara, Calif.
The chamber clusters in a cluster tool are typically arranged by function with related functions being in separate clusters. For example, in the Endura cluster tool used for metal deposition, there is a pre-metallization cluster where the wafers are admitted, oriented, degassed, sputter cleaned, subsequently cooled down and removed from the apparatus and at least one metallization cluster of process chambers wherein metal deposition, e.g., copper deposition, is performed. The various chambers of the pre-metallization cluster are serviced by a centrally located robotic transfer mechanism that is enclosed in a buffer chamber. Similarly, the process chambers of the process cluster are serviced by a centrally located robotic mechanism that is enclosed in a transfer chamber. Connecting these two clusters are transition chambers for moving the wafers between the metallization and pre-metallization clusters. These transition chambers are typically utilized for comparatively uncomplicated operations such as precleaning of the wafers prior to processing and cool down of the wafers after processing.
Copper is typically deposited onto wafers in such cluster tools by chemical vapor deposition ("CVD") in a sequence of process chambers to build up a plurality of layers. A layer of CVD copper may also be used as a seed layer for electroplating or as a seed layer for copper deposited by physical vapor deposition ("PVD"). Generally, copper is deposited using a PVD process when it is desired to deposit copper at low temperatures. All of these copper deposition processes have experienced problems with adhesion of the copper to the substrate.
Several possible solutions to the problem of poor adhesion have been proposed. One of these proposed solutions is to initially deposit a copper layer by physical vapor deposition ("PVD") (i.e., PVD copper) as a seed layer. PVD deposition is performed using a magnetron sputtering process by placing a copper target above the wafer substrate, providing a gas, such as argon, between the target and the substrate and exciting the gas with a high-voltage DC signal to create ions that strike the target. As the target is bombarded by ions, copper atoms are dislodged and become deposited onto the substrate. The dislodged copper atoms generally have substantial kinetic energy and when they impact the substrate the atoms tend to strongly adhere to the substrate.
While the thin layer of PVD copper provides the necessary adhesion, the PVD process does not provide sufficient step coverage to permit the PVD process to be used for bulk copper deposition. As such, the bulk copper deposition is accomplished by an electroplating or a CVD process. Because PVD deposition and either electroplating or CVD deposition cannot be accomplished in the same chamber, an additional chamber must be added to the cluster tool's metallization cluster. As such, deposition of such a PVD seed layer would require the sacrifice of one of the processing chambers in the process cluster of a cluster tool to make room for the additional PVD chamber. This would adversely affect the throughput of the cluster tool since such a chamber would ordinarily be utilized for a more demanding and/or time-consuming CVD process step.
Furthermore, an additional chamber would require approximately 10 seconds to position a wafer in the chamber and ready the chamber for deposition. As such, the additional chamber would adversely impact throughput of the system. Also, an additional chamber adds substantial cost to a system.
Therefore, there is a need in the art for a modified cluster tool and a method of utilizing such a modified cluster tool that provides for PVD seed layer deposition without replacing a CVD or electroplating chamber in the cluster tool.